I had green caterpillars eating holes in the leaves of my broccoli and brussell sprouts. Since they are all the same species, perhaps that is what you have? They blended in really well and were tough to spot when they were small, but became more obvious as they grew. I usually found them on the inner leaves. I just picked them off manually and have seen no new caterpillars or leaf damage for weeks.

It's a cabbage looper. Use Bacillus thuringiensis against them if hand picking isn't practical. Bacillus thuringiensis (BT) is simply a bacteria that likes eating caterpillars. It is sold as Dipel or Thuricide. Here is a link on cabbage loopers

If you can see the green caterpillar then most likely it's the cabbage looper. Sometimes called an inchworm. I just flick them off into a coffee can with some detergent and water. You can use BT which kills them by being systemic. That means it is actually inside the plant and the plant is now deadly to the worm. I've never used it since it MUST have some effect on the rest of the world. I'm probably being a bit paranoid there. Try the detergent first. The damage to your plant, going by the picture, isn't severe as yet. By the way, those cute little white butterflies we see all summer are the culprit. Some people spray a little cheap vanilla extract on the plants and it seems to confuse the butterfly (moth). They go everywhere and apparently recognize your brassicas by aroma. Makes sense. Then they lay their eggs and along comes the hungry caterpillar. Hope all this helps somewhat. Best wishes with your plants.

Traps, secured to a wire which is attached to a concrete block, the dead weight to avoid the rat getting away if only partially trapped. Bait with a small piece of nutmeat, lightly topped off with a smidge of peanut buter. For the first several days, just bait the trap but don't set it. Then, day 3, bait and set the trap. Beause rats quickly learn to avoid traps, set out multiple baited traps. Then on day 3 (as said above) bait and set all of them.